1. Field of the Invention
This invention pertains generally to digital photography, and more particularly to a camera configured for simulating long exposure still pictures.
2. Description of Related Art
Long exposure-time still images (long exposure images) have long been used for creating artistic effects, such as in representing motion, smoothing motions, and for isolating a stationary subject. Since the aperture must be left open for a significant period of time, it is difficult or even impossible in some circumstances for a consumer to take a long exposure still picture without the assistance of a tripod. In addition, the camera controls necessary for creating a useful long exposure image are often only available on high-end single-lens reflex (SLR) cameras. The average consumer taking occasional photos usually prefers not to be burdened with carrying a tripod, or trying to figure out the nuances involved in creating long exposure images and thus is not able to take advantage of their creative possibilities.
FIG. 1 depicts the conventional process 10 for obtaining a long exposure-time image. A camera device 12 is retained on a steady rest 14 (e.g., tripod and typically with a remote shutter control (not shown)). The camera aperture is set for a given small aperture size and a long exposure interval 16. It will be noted that to create a long exposure photograph with a conventional still camera the light-sensing elements are exposed to light from the scene for the duration of the exposure, which can span from fractions of a second to minutes, or even hours.
To prevent unintentional blurring of stationary scene content when taking conventional long exposure images, the camera must be maintained very still during exposure. For relatively short exposures, for example as long as about 1/60th of a second, a person without benefit of a stationary mount (e.g., tripod) can maintain themselves sufficiently still to prevent the blurring which results from camera shake. Slightly longer exposures are possible with various camera stabilization technologies such as Sony's Super SteadyShot®. However, for longer exposures, a tripod becomes necessary to prevent blurring of the static regions of the scene. Rapidly moving objects may still exhibit camera shake induced motion blur, regardless of how steady the camera is maintained.
It should be appreciated that the term “exposure”, as used in photography, describes the total amount of light allowed to fall on the image sensor (or photographic medium) while the shutter is open. Exposure is typically measured in lux seconds, and can be computed from exposure value (EV) and scene luminance over a specified area.
The term “long exposure” is a term of photographic art often referring to the technique of selecting a shutter speed which is much slower than necessary for the given light conditions toward providing a desired photographic effect. For example, although an image could be captured with a 1/100th of a second exposure at a first aperture setting, the photographer chooses an exposure time of ½ second to 10 seconds and a much smaller second aperture setting. The term “long exposure” is generally used herein to mean an exposure duration which is not readily achieved without the need of a tripod and/or other equipment, and is contrasted to “short” or “normal” exposure times which can be generally obtained without the need of a tripod or other steady mount.
Long exposure images are captured for any of a number of purposes. One such purpose for long exposure images is that of artistic blur, in which stationary parts of the scene retain perfect detail while moving parts of the scene are motion blurred. Photographers have used this technique to create dramatic results, including: (1) creating a misty, cloudy, or creamy effect for moving water, such as waterfalls or fountains; (2) to “bring out” a stationary subject in a dynamic environment by allowing motion blur to de-emphasize the moving objects; (3) to draw a contrast between stationary and moving parts of the scene; (4) to exaggerate the apparent speed of a moving object, or objects; (5) to create special lighting effects, such as streaking headlights or taillights of automobiles, and to provide other dramatic effects. Examples of some of these effects are shown in a later section.
Another purpose for long exposures is to increase the signal to noise ratio and thus improve image quality. The extension of the exposure time increases the signal strength relative to the noise, leading to “cleaner” higher quality images and is particularly well suited for photographs taken in very low-light situations. This effect is most dramatically seen when used in low-light conditions in which available signal strength is low.
As a practical matter, many consumers or other amateur photographers never bother with taking long exposure pictures in view of the difficulties involved. Barriers to consumer creation of long exposure pictures include the following. (1) The burden of carrying a tripod and/or associated accessories such as a shutter release cable or remote control. (2) Many situations and environments are not amenable to the use of tripods, such as on a busy sidewalk, from a moving vehicle and so forth. (3) The user may have never learned, or may not remember, how to effectively create long exposures. (4) It often requires a great deal of experimentation (many attempts) for an amateur to obtain useful results.
Accordingly, a need exists for a system and method of automatically creating long exposure images with less equipment and difficulty. These needs and others are met within the present invention, which overcomes the deficiencies of previously developed camera systems and methods.